Large femoral heads are increasingly being used in total hip replacement procedures. Some advantages of using a large femoral head are a reduced dislocation rate and reduced impingement between a femoral neck of a hip replacement prosthesis and a corresponding acetabular cup edge.
However, a disadvantage of the use of large femoral heads is intermittent groin pain, thought to be due to interference with a free excursion of a psoas tendon. As illustrated in FIG. 1, a psoas muscle 10 takes its origin on the lumbar spine 12, a tendon 14 of psoas passes over the front of the bony pelvis 16, the hip joint 18, the femoral head 20 and the antero-inferior femoral neck 22 before insertion into the lesser trochanter 24. The action of the psoas muscle 10 flexes the hip joint 18.
Small femoral heads that have hitherto been used as prosthetic heads on a total hip replacement femoral stem have been of a mono-block construct. Large metal femoral head prostheses are commonly not mono-block constructs as designers and manufacturers seek to reduce the weight inevitable with the use of solid metal components. Commonly, large femoral head components are partially hollowed out to reduce weight with a tapering neck of a femoral stem engaging in a correspondingly tapered female recess in the femoral head component. Even more commonly, a sleeve is employed over the neck to reduce the inventory of femoral head components needed for a hip replacement operation (with multiple lengths and, in certain designs, offsets being available through the use of different sleeves).
FIG. 2 illustrates a known femoral implant design 30 comprising a femoral head 32, a conical sleeve 34, and a femoral stem 36. The femoral head 32 is constituted by a partially hollowed out part-spherical metallic component with an inwardly tapering channel 38 provided approximately at its centre, for receipt of the sleeve 34 therewithin. The femoral stem 36 comprises a elongated portion 40, which generally tapers away from the femoral head 32 and terminates in a rounded tip 42, an intermediate portion 44, having approximately straight parallel sides 46, and a neck portion 48, which extends in an offset antero-inferior direction and terminates in a conical taper 50 which is received within the sleeve 34. As illustrated, the femoral head 32 comprises a relatively thin depending edge or skirt 52 which surrounds the interconnecting channel 38, sleeve 34 and conical taper 50 but which is spaced therefrom to accommodate a portion of a patient's resected femoral neck to secure the implant on the patient's femur.
It has, however, been found that groin pain is commonly associated with the use of such hollowed-out femoral heads, like that illustrated in FIG. 2.
It is therefore an aim of the present invention to provide an improved femoral head prosthesis.